A means of fabricating integrated optical components is by the deposition of doped silica waveguides formed on a doped silica film deposited on a silicon substrate. This technology, referred to "silica on silicon," has the potential to make optical devices that are smaller in size, are of greater complexity, and are potentially lower in cost than discrete optical devices which are fabricated from fiber and micro-optic components.
A variety of passive optical components have been made using silica on silicon technology in which optical waveguides are formed using a phosphosilicate glass (P-doped silica) core. In one fabrication method, the waveguides are deposited on a base layer called "hipox" formed by the oxidation of silicon under high pressure steam. The core is then covered with a thin cladding layer of SiO.sub.2. Device built using this technology include compound Bragg reflectors, multiplexers, adiabiotic polarization splitters, and array star couplers.
At the present time, phosphosilicate glass core waveguides of integrated optical devices made using silica on silicon technology are normally butt coupled to input-output optical fibers by means of a bonding material such as an epoxy, UV-adhesive and/or, in some instances, a potting material. The substance used to join the waveguides of the optical device to an optical fiber also serves the necessary step of filling in gaps which may exist at the butt coupling. However, in those applications where the failure of the bonding material or deterioration of its optical properties can result in extremely expensive repairs, such as in undersea cable applications, the use of these materials is not acceptable.
The publication entitled "Fiber Attachment for Guided Wave Devices", by E. J. Murphy, Journal of Lightwave Technology, Vol. 6, No. 6, June 1988, presents a review of the status of fiber attachment to guided-wave devices. Current methods for achieving low fiber-to-waveguide-to-fiber insertion losses are discussed and techniques for aligning and permanently attaching fibers are described.
In this publication the author asserts that an appropriate bonding material and method of application is critical as it determines the stability and reliability of the fiber-waveguide joint. He notes that UV curing adhesives are widely used because they can be cured rapidly without compromising the fiber alignment. However, UV-adhesives have questionable stability when subjected to environmental extremes in temperature, pressure or humidity and therefore, the joints may not be sufficiently stable. Equally important, even a slight deterioration in the optical properties of the epoxy will seriously impair the transmission of optical signals through it.
The publication concludes with the statement that a major challenge of the next decade will be to develop a reliable and robust fiber attachment and packaging technology.
The invention here disclosed is specifically directed toward solving this problem by providing a reliable and robust fiber-waveguide butt coupling arrangement which can be used in all environment and applications, including undersea applications.